Method of working beryllium



nite States 2,872,363 METHOD OF WORKlNG BERYLLIUM 11 Claims. (Cl.148-115) are Thisinvention pertains to the fabrication of berylliummetal into various shapes and forms and more particularly to a methodwhereby beryllium metal is fabricated into sound rods, sheet, and foilhaving predetermined favorable, physical and mechanical properties.

The process of this invention is particularly useful in the fabricationof beryllium destined for use as a moderator in a chain-reactingneutronic reactor Where it is of primary importance that the metal usedtherein have certain physical and mechanical properties as well as thenecessary purity.

It is an object of this invention to provide a method for thefabrication of beryllium metal whereby fabricated shapes havingpredetermined favorable physical and mechanical properties such astexture, hardness, ultimate strength and reduced cross-sectional areamay be produced.

It is a further object of this invention to provide a method wherebyberyllium metal can be deformed to a state wherein substantial reductionof cross-sectional area can be obtained without sacrifice in the qualityof surface structure or mechanical properties.

It is a further object of this invention to provide a method for thefabrication of beryllium metal into sheets and foil having a brightfinish and a fine texture free of cracks.

It is a further object of this invention to provide a method wherebyberylliummetal can be measurably reduced in cross-sectional area to formrods or tubes which are unmarred by cracks, scams or scores.

It is a further object of this invention to provide a method wherebyberyllium can be protected during the deformation process from theeffect of contact with the deforming apparatus.

, Other objects and'advantages will become apparent'to those skilled inthe art upon further examination of this specification.

. Heretofore, beryllium metal has beensuccessfully deformed only attemperatures exceeding the recrytallization temperature. For berylliummetal, the lower limit of recrystallization is about 700 C., but may behigher in the absence of prior working.

I have discovered that beryllium metal, preferably that having a refinedgrain obtained by prior working above the recrystallization temperature,can be successfully fabricated at a temperature between 300 and 400 C.by such processes of plastic deformation as extrusion, rolling, forging,swaging, and drawing. Beryllium metal mechanically worked according tothe process of this invention within the 300 to 400 C. temperature rangeto eifect plastic deformation has a texture, preferred orientation, andphysical and mechanical properties equal or superior to those of metalworked at temperatures substantially higher than the recrystallizationtemperature.

Studies of the ultimate strength, elongation and reduc tion in area as afunction of temperature show that a maximum ultimate strength ofapproximately 38,000 p. s. i. is attained at about 200 C. from whichpoint the ultimate strength decreases linearly with an increase intemperature. However, the values fortensile strength at temperaturesbetween 300 and400" C. do not go below about 28,000 p. s. i. Within the300-400 C. temperature range beryllium metal is suificiently ductile foroperations such as extrusion or rolling. The elongation reaches a valueof 24 to 26 percent in the 300 to 400 C. temperature range and drops offwith an increase in temperature above 400 C. Although reduction-inareavalues reach a maximum at temperatures above 400 C., this effect isoffset by the disadvantage of necking down, that is, the contractionarea tends to concentrate at one point on the bar because at thistemperature range the plastic flow occurs only locally. However, at 300to 400 C., stretch and plastic flow extend over the entire gauge lengthand no necking down is observed, while as much as 24 to 32 percentreduction can be achieved by working within the 300-400 C. temperaturerange.

Hardness values of extruded material show that this property is afunction of the extrusion temperature in that the hardness of thedeformed metal varies inversely with the temperature of extrusion.Moreover, studies of the torsion properties of beryllium as a functionof temperature show that the strength of the beryllium decreasesapproximately linearly with increase in temperature. In addition, theobserved type of break which occurs between room temperature and 200 C.is helicoidal, while the break occurring in metal treated attemperatures of about 300 C. and above is the transverse type.

In addition to the improved mechanical and physical properties observedin beryllium metal fabricated at temperatures between 300 and 400 0,working beryllium metal within this relatively low range has the addedadvantage that at such temperatures beryllium is relatively inert toatmospheric oxidation so that the use of an inert or non-oxidizingatmosphere, such as helium, argon or hydrogen, is not necessary.Moreover, by working within this relatively low temperature range, thetensile strength of the deforming apparatus, for example a mandrel, isonly slightly affected.

in practicing my invention, beryllium metal is heated to a temperaturebetween 300 and 400 C. after first cleaning it in hot nitric acid andcutting it to a size suitable for rolling. After the-initial heating ina suitable container, the heated billet or sheet is passed throughrolls, the distance between the top roll and the bottom roll beingcapable of adjustment after each pass according to an arbitrary amount,such as 002", until the thickness desired is attained.

If the rolls are not heated to the temperature necessary for the rollingof the metal, the metal can be restored to the desired rollingtemperature by reheating between passes. About 3 minutes are required toreheat a jacketed billet as jacketing' (as set forth in another portionof this specification) tends to preserve the rolling temperature. Inrolling billet-s through heated rolls some cooling may be necessaryfollowing each pass since the temperature of the metal-may rise as theresult ofworking in the rolls. However, in any event the Working ofberyllium undergoing the deformation process should be effected asnearly as possiblewithin the 300 to 400 C. temperature range.

Rolling within this low temperature range of 300 to 400 C.'may also becombined with the steps of periodically annealing at a temperature abovethe recrystallization point. However it must be kept in mind that inusing unjacketed beryllium, the annealing and subsequent cooling to theworking temperature must be carried out in a non-oxidizing atmosphere,or, if oxide is formed during annealing, it must be removed prior toreworking at 300 to 400 C.

In the fabrication of beryllium at temperatures between 300 and 400 (3.,the, use of a protective metal coating may beomitted. In one embodimentof this 'invention unjacketed beryllium is fabricated into sheets byheating to a temperature between 300 and 400 C. and then immediatelypassing it through rolls heated to about 400 C. and annealingperiodically in a nonoxidizing atmosphere, such as hydrogen, at atemperature of about 800 C. or at some temperature above theternperature of recrystallization. The metal is then cooled to at leastbelow 600 C. in a non-oxidizing atmosphere or it may be water-quenchedfrom the annealing temperature. Any subsequent working is carried out at300 to 400 C. The subsequent annealing at high temperatures of metalpreviously worked at temperatures between 3004-00 C. is not absolutelynecessary as better than 50 percent reduction in area can be attainedsolely by fabrication within the BOO-400 C. temperature range.

In processes using rolling between heated rolls at 400 C. followed byperiodic annealing at 800 C. in the presence of hydrogen, the reductionper pass has usually been from 5 to percent, and up to 50 percentreduction in area can be attained between annealing periods Withoutadversely affecting hardness values. In addition to attaining greaterreduction in area and strain-hardening by periodic annealing as setforth herein, the annealing subsequent to cold-working at 400 C.materially increases the ductility, ultimate strength, and elongation inthe metal.

As shown in Example II, beryllium metal can be extruded Without the useof a protective jacket. However, for the same reasons set forth in thediscussion of metal coverings in another section in this specification,a protective metal covering is more commonly used in the extrusionprocesses.

A typical extrusion operation, according to a preferred embodiment of mymethod, comprises encasing a billet of beryllium, having an improvedgrain refinement over the cast ingot, with a low-carbon steel jacketwhich is drawn to size and in which the wall thickness on all sides issuitably from about 0.1" to .02". The encased beryllium billet is thenplaced in a soaking furnace, e. g. for about one-half hour for billetsmeasuring from 2 to 3" in length and .945" in outside diameter. Thecontainer and stem are also preheated to a temperature within thetemperature range used for working according to the process of thisinvention, namely 300 to 400 C. The die is suitably lubricated andfitted With a copper nib machined to fit the conical portion of the die.The billet is then inserted and extruded under a pressure preferably ofabout 50 to 100 tons per square inch. Such a pressure is suitable whereextrusion is made through a conical die having about a 120 includedangle and a diameter of at least .335". A nominal reduction in area ofabout 8:1 is achieved by extrusion within this temperature range underthese conditions of pressure and type of apparatus. However, it will beapparent to those skilled in the art that the combined factors ofextrusion, pressure, rate of flow and deformation defined by thereduction in area all contribute to the fabrication of beryllium metal,and variations in these factors which affect the ultimate factor of theextrusion temperature are intended to be included within the scope ofthis invention.

It will be noted as shown in Example II that the above process forextrusion is applicable to the fabrication of tubes as well as rods. Theonly alteration necessary for the extrusion of rods is that a hole isdrilled in the beryllium billet prior to jacketing. A sleeve consistingof a suitable protective metal such as copper is fitted into said holein order to provide lubrication between the mandrel and the berylliummetal undergoing deformation.

In a further embodiment of this invention, a protective metal coatingfor the beryllium metal undergoing fabrication is used. In thisembodiment, beryllium is enclosed within a metallic covering or jacketwhich serves as a buffer material between the deforming apparatus andthe refractory beryllium metal being subjected to treatment. The use ofa metallic jacket extends the life of the die, especially where numerouspasses through the deforming apparatus are required. The protectivemetal jacket also serves as a lubricant and preserves the billet fromgalling and scoring during extrusion or edgecracking from rolling. Inaddition the metal jacket reduces the coefficient of friction developedbetween the die surface and the beryllium metal thereby affording ameans for controlling the temperature of the billet and also preventingundue heat losses by direct exposure of the billet to cooling surfaces.

The jacketing material should be of such metal composition as to beductile and formable when subjected, as .a composite with the berylliummetal, to the deformation processes. The enclosing metal should also notalloy with the beryllium at the fabrication temperature so that it iseasily removable from the billet. However, at the temperatures used inthe process of this invention, the tendency for beryllium to alloy withthe jacketing material, even copper, is virtually negligible. By rollingat 300400 C., the stainless steel jackets do not require as frequentreplacements as in rolling at temperatures of 700 C. or above.

Coating materials may be of either the ferrous or nonferrous type.Jacketing material which have been successfully used in the process ofthis invention are copper, low-carbon steels, stainless steel containingnickel and chromium, e. g. Monel and 18-8. For rolling purposes,jacketing of beryllium may be effected by slipping the beryllium into aformed steel tube having a wall thickness of about A3" or less andwelding steel caps of about the same thickness to each ,end. A berylliumslab or sheet may also he slipped between a folded sheet of protectivemetal jacketing material for rolling foil or the beryllium billet orsheet may be spray-coated with the protective metal.

The following examples will illustrate the preferred embodiments of thisinvention.

EXAMPLE I Rolling of beryllium Beryllium stock measuring .004" x 2.5 x2" which had been previously hot-rolled at 800 C. from one inch rodextruded at 1000 C. and had been reduced in crosssectional area by aratio of 16:1 was first pickled in hot nitric acid. The clean berylliumsheet was then slipped between a folded sheet of 18-8 stainless steel ofhi thickness and was heated in an electric furnace to 350 C. Thediameter of the roll was 8.75" and the speed was 40 R. P. M. with areheating time of three minutes following each pass, seven passes in allbeing necessary to reduce the beryllium from a thickness of .004 to.002", thereby forming beryllium foil which was free from holes andcracks and having a bright surface. The rolling data are as follows:

Gauge, Reduc- Beryllium Pass inches tion, Thickness,

inches inches 1 Distance from top of bottom roll to bottom of top roll.2 Amount of reduction in gauge. Does not take into considerationspring-back in metal or spring in rolling mill.

The .002"-foil produced by the rolling treatment just outlined wasenclosed in a sheet of stainless steel .065" thick and subjected torolling under conditions identical with those used for the first sevenpasses just described.

Gauge, Reduc- Beryllium Pass inches 7 tion, Thickness,

i inches inches EXAMPLE II Extrusion of beryllium- Billets of berylliumpreviously extruded at 1000" C. with a 16 to 1 reduction to refine thegrain were reextruded into rods and tubing at 350 C. in a l00-ton Versonpress. Both jacketed and unjacketed billets were tested. Copper andlow-carbon steel were used as jacketing. materials.

The dimensions of billets used in fabricating rods ranged from 2 to 3"in length and the core outside diameters were from .925" to 0.945. Thesebillets were jacketed in copper or steel having a wall thickness ofabout .010. Rods were extruded through a 120 included angle conical die,the die being at least .355" in diameter. 7

For tube fabrication, holes measuring .025" (inside diameter) weredrilled in billets 3" long and .930" wide and these billets were thenfitted with a copper sleeve of- .016" thickness and an inside diameterof .215 to accommodate the mandrel, which measured .200" in. diameterwith a taper of 0.002" per inch. Tubing was formed by using a.500"-diameter die.

The container and stem were preheated to 350 C. and the billets wereheated to 350 C. and permitted to soak for one-half hour prior toextrusion. The container was; loaded for extrusion in the followingorder: The die was lubricated with heavy oil; a copper nib machined tofit the conical portion of the die was placed on the die; the

EXTRUSION OF RODS billet was "inserted and a graphite cut-oii'measuringapproximately one inch was placed on top of the billet after'whichthebillet was extruded. In order to prevent fracture of rods subsequent totheir emerging from the press, a substantial number of asbestos sheetswas placed in the pit beneath the press to break the shock as the rodfalls into the pit.

In general it may be said that the processes disclosed in the presentapplication areillustrative rather than limiting in scope and that allof the numerous equivalents and modifications which would-naturallyoccur to those skilled in the art will be included in the scope of thepresent invention. Only such limitations as are indicated in theappended claims should be imposed on the scope of this invention.

What is claimed is:

1. A method of working beryllium metal comprising subjecting berylliummetal to plastic deformation at a temperature between 300 and 400 C.

2. The method of claim 1 wherein the plastic deformation is effected ata temperature of about 350 C.

3. A process of working beryllium metal comprising extruding berylliummetal at a temperature between 300 and 400 C.

4. A process of working beryllium metal comprising rolling said metal ata temperature between 300 and 400 C.

5. A process of fabricating beryllium metal comprising covering saidberyllium with another metal thereby efiecting a jacketed billet, saidjacketing metal being formable at temperatures between 300400 C. andnon-alloying with beryllium at said temperature range, and subjectingsaid jacketed billet to plastic deformation at temperatures between 300and 400 C.

6. The process of working beryllium metal comprising jacketing saidberyllium with copper thereby forming a unitary billet and extrudingsaid copper jacketed beryllium at a temperature between 300 and 400 C.

7. The process of Working beryllium metal comprising jacketing saidberyllium with stainless steel thereby forming a unitary billet andextruding said jacketed beryllium at a temperature between 300 and 400C.

8. A process for working beryllium metal comprising jacketing said metalwith stainless steel and rolling said jacketed billet at a temperaturebetween 300 and 400 C.

9. A process for working beryllium metal comprising subjecting berylliummetal to a process of plastic deformation at a temperature of 300400 C.and subsequently annealing periodically said deformed metal at atemperaturein excess of the recrystallization temperature.

10. The process of claim 9 wherein annealing takes place at atemperature of at least 700 C.

Billet Container Diameter Diameter Jacketing Material Temp, Temp, ofDie, of Reduc- Pressure, Remarks Used 0. 0. inches Mandrel, tionlbs./sq.in.

inches Copper 350 350 .500 4:1 153, 000 Jacket was continuous andsmooth. Only slight shallow seams visible on extruded rod.

Steel 350 350 .500 4:1 154,000 Steel jacket ruptured during extrusionbut beryllium surface showed only shallow seams.

N Ja ket 350 350 .355 7. 9:1 191, 000 Leading third and trailing third"rattlesnaked" but middle third was sound. Die surface showed scores.

Steel 350 350 .355 7. 9:1 229, 000 Steel jacket ruptured duringextrusion.

EXTRUSION OF TUBES Copper (20 mils) 350 350 .500 .200 4. 6:1 153, 000Satisfactory-m0 scoring observed.

Copper (18 mils) 350 350 .500 .200 4.621 153,000 Tube surfacesatisfactory-no scoringtube extruded easily.

Copper (15 mils) 350 350 .500 .200 4. 6:1 153,000 Tube extruded easily,but outer surface was slightly scored in one area.

11. A process for working beryllium metal comprising subjecting an ingotof beryllium to heat treatment at a temperature above therecrystallization temperature, cooling said recrystallized metal andreheating said recrystallized metal to a temperature between 300 and 400C. and subjecting said metal to plastic deformation at a temperaturewithin,300 and 400 C.

References Cited in the file of this patent UNITED STATES PATENTS1,547,395 Hoyt July 28, 1925 3 1,597,189 Gero Aug. 24, 1926 2,384,351Slagle Sept. 4, 1945 FOREIGN PATENTS 5 550,110- Great Britain Dec. 23,1942 OTHER REFERENCES Raynor: Journal of the Royal Aeronautical Society,vol. 10 50, pp. 390-415 (1946).

